I'm actually looking for local hardware solutions.

Sending every change to everything up to AWS would be wildly expensive both in bandwidth and cash. It would also put all of your data "in the cloud" (aka on other people's computers).

Plus a ransomware attack on AWS would make the backup unavailable.

A small, local device that contains a memory cache could write a DVD once half the cache is filled (double buffering).

A double-sided, double-layer DVD can hold 16GB so an "inline cache" with 32GB could copy and store a DVD worth of disk backup and then write a DVD.

BLU-RAY can store up to 50GB